[UNIX] Canonicalization and Directory Traversal in iSeries FTP Security Products

From: SecuriTeam (support_at_securiteam.com)
Date: 04/25/05

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      Canonicalization and Directory Traversal in iSeries FTP Security Products
    ------------------------------------------------------------------------

    SUMMARY

    The IBM iSeries (AS/400) server provides a "unified access scheme, called
    IFS, to all of the files and to all of the database tables in all of the
    database libraries".

    Because the built-in FTP server provides full access to the IFS, a valid,
    authenticated user, can access and retrieve via FTP all of the database
    tables and all of the files that he has authority to access, based on the
    server assigned object authority.

    DETAILS

    The problem is usually addressed by third party iSeries security products
    that attempt to limit FTP users only to the assets they should have access
    to.

    For example, these products supposedly can limit access to a folder called
    /home/bp/outgoing, so while getting a file called
    /home/bp/outgoing/dailysales.csv is allowed while getting a file called
    /qsys.lib/aplibf.lib/apcaccp.file/apcaccp.mbr is blocked.

    Several iSeries security products have been found to be vulnerable to a
    canonicalization attack resulting in a possible unauthorized access to
    iSeries database tables that were supposedly blocked from access.

    For example, these products allows this FTP command:
    GET
    /home/bp/outgoing/../../../qsys.lib/aplibf.lib/apcaccp.file/apcaccp.mbr

    The following iSeries security vendors were approached to see whether
    their products are vulnerable to this canonicalization attack:
    RazLee: notified on Feb 15, fix is available.
    Castlehill: notified on March 15, fix is available.
    Powertech: notified on March 15, fix is available.
    Bsafe: notified on March 2, vendor has no comment.
    SafeStone: notified on March 15, no reply received.
    NetIQ: notified on March 15, no reply received.

    iSeries servers without FTP security protection are vulnerable by default.

    ADDITIONAL INFORMATION

    The information has been provided by <mailto:shalom@venera.com> Shalom
    Carmel.
    The original article can be found at:
    <http://www.venera.com/downloads/Canonicalization_problems_in_iSeries_FTP_security.pdf> http://www.venera.com/downloads/Canonicalization_problems_in_iSeries_FTP_security.pdf

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